The scope of this paper is to show how digitized, structured data, as a combination of design data, operational data, riser analyses and measured riser response can be used to enable drilling operations on a subsea exploration with well challenging soil or/and harsh environmental conditions. The structural integrity of the well foundation and soil support has been verified by combining the structured data obtained from measurements with the design information. A sensor system has been fitted to the riser and BOP on mobile drilling units to monitor soil and structural integrity. The combination of pre-operational assessments and monitoring during operations has been carried out for 7 consecutive drilling campaigns, with two different semi-submersible drilling rigs. The work presented in this paper will give a comparison between the measured response and the up-front design analysis, and show show to combine the design information with operational data and measured response to enable future operations. During the design phase of a subsea exploration well a wide range of design assumptions must be considered. The range in high and low estimates for parameters such as soil support or riser and BOP mass and damping forces may be considerable. In general conservative parameters must be selected, leading to worst case scenarios, which again may lead to limited operational windows, introduce high cost mitigating actions or in worst case prevent operations from being carried out. This paper will present the benefit of using actual measured response and operational parameters back into the design loop when planning upcoming drilling campaigns. Structured operational data and measured response is used to improve analysis models; which lead to reduced conservatism. For cases of re-entry on an existing exploration well with heavier equipment, the measured soil support can be used to rule out some worst-case scenarios, and enable the upcoming operation. A case example of an exploration campaign enabled by the design loop will be shown.

Subsea exploration well systems are subjected to complex loading due to vessel motion and hydrodynamic forces on the riser. In design of the wells, both the ULS/ALS design under extreme loading and fatigue design under operational loading are heavily dependent on the soil support along the uppermost 20 m of the conductor casing. In today’s practice, design of the conductor against extreme loading is typically performed using the soil reaction curves (p-y springs) recommended in API RP 2GEO [1]. In recent years, 4Subsea have been monitoring the BOP and riser responses during exploration drilling campaigns for Lundin Norway. The purpose of these monitoring campaigns is to track the performance of the wells with time, based on integrity parameters such as well stiffness, BOP resonance frequency and BOP motion rotational depth. This paper summarizes the monitoring results from seven well locations in the North Sea and the Barents Sea. The observed well response is compared with up-front design analyses. The discrepancy between up-front design analyses and the observed performances is discussed in light of the uncertainties associated with the geotechnical input parameters and soil reaction models. The purpose of the paper is to reflect on the challenges faced with exploration well design and highlight areas that improvements can be made.

Structural monitoring of subsea structures is very common in the oil and gas industry. Monitoring may be performed to keep track of e.g. position, movements, loads and fatigue accumulation. Well growth of subsea wells is a slow process, and traditional accelerometer-based monitoring is not feasible. The objective of this paper is to present the camera-based monitoring campaign of the subsea wellheads on the Norwegian continental shelf. The paper gives a brief introduction to the issue around well growth and how that potentially can lead to fatigue issues. Further we give an overview of the theory behind marker-based monitoring and explain how this is used in practice by presenting experience from a measurement campaign where 2 different battery powered camera kits operated subsea for 5 months. This to enable establishment of the fatigue integrity of the subsea wellheads. The paper will show how the experience from this campaign has been used to create a new and improved camera kit for more efficient monitoring of similar issues in the future. The technology can be used in a wide range of subsea applications for monitoring slowly variating relative displacements.